Adhesive for low temperature applications

ABSTRACT

Adhesive compositions are made from methacrylate ester monomers, elastomeric polymers having a Tg below -25° C. and which are soluble in the monomers, core-shell polymers which swell in the monomers but do not dissolve therein, and free radical producing catalysts. These adhesive compositions when used in bonded assemblies exhibit a combination of high adhesive bond impact strength and high bulk tensile elongation.

BACKGROUND OF THE INVENTION

The field of art to which this invention pertains is structural acrylicadhesives.

Structural acrylic adhesives are rubber-toughened adhesive systems thatcure rapidly at room temperature to give excellent adhesive properties.Such adhesives are characterized by high peel strength, shear strengthand chemical resistance. They are also tolerant of a variety ofsubstrate surface contaminants, such as oil.

Fast curing adhesives are described in U.S. Pat. No. 3,832,274. Theseadhesives are made from elastomers having Tg of less than 15° F.,acrylic monomers and a redox catalyst.

Structural adhesives which contain chlorosulfonated polyethylene orsulfonyl chloride and chlorinated polymers are disclosed in such patentsas U.S. Pat. Nos. 3,890,407, 3,962,372 and 4,287,106.

U.S. Pat. Nos. 4,126,504, 4,348,503 and 4,451,615 disclose variouscombinations of elastomers, acrylic monomers, catalysts and otheradditives.

Adhesives based on diene polymers, such as polybutadienes,polyisoprenes, butadiene-styrene copolymers and ABS graft polymers, plusvinyl monomers, adhesion promoters and the like are described in U.S.Pat. No. 4,287,106.

Methacrylate based adhesives which contain chlorinated orchlorosulfonated polyethylene polymers and graft copolymers of thecore-shell type are disclosed in U.S. Pat. No. 4,536,546.

With the use of more and more plastics in structures, e.g., automobiles,there is a continuing and even increasing need for adhesives which canbe used on plastics as well as metals to form bonds which will hold upunder a wide variety of adverse conditions.

There is a particular need for structural adhesives which not only havehigh adhesive bond impact strength but also have high bulk tensileelongation when measured at low temperatures.

SUMMARY OF INVENTION

This invention is directed to structural adhesive compositions. In oneaspect, this invention pertains to structural adhesives which have highadhesive bond impact strength. In another aspect, this invention relatesto structural adhesives which have high bulk tensile elongation whenmeasured at temperatures of -10° F. (-23° C.) or lower. In still anotheraspect, this invention relates to structural adhesives, the bulk tensileelongations of which are largely reversible even at low temperatures.

The adhesive compositions of this invention are comprised of:

(A) a methacrylate ester monomer;

(B) an elastomeric polymer soluble in the ester monomer, said polymerhaving a Tg below about -25° C.;

(C) a core-shell graft copolymer which swells in the monomer but doesnot dissolve therein; and

(D) a free radical producing catalyst.

The adhesive compositions of this invention, when used in bondedassemblies, exhibit a combination of high adhesive bond impact strength(at least 15 ft-lb/sq.in.) and high bulk tensile elongation (greaterthan 10 percent) when measured at -10° F. (-23° C.) or below.

DESCRIPTION OF THE INVENTION

The monomers useful in this invention are methacrylate ester monomerswherein the alcohol portion of the ester group contains one to eightcarbon atoms. Examples of such ester monomers are methyl methacrylate,ethyl methacrylate, 2-ethyhexyl methacrylate, cyclohexyl methacrylateand mixtures thereof. The preferred ester monomer is methylmethacrylate.

Additional monomers which can be used in combination with themethacrylate monomers are acrylate esters wherein the alcohol portion ofthe ester contains 1 to 8 carbon atoms, examples of which are methylacrylate, ethyl acrylate, butyl acrylate and 2-ethyhexyl acrylate. Otheruseful monomers are acrylonitrile, methacrylonitrile, styrene, vinyltoluene, and the like.

The useful monomer composition contains at least about 50 weight percentmethacrylate monomer and, preferably, at least about 50 weight percentmethyl methacrylate monomer.

Additional monomers which are used in combination with the methacrylateester monomers are free radical polymerizable ethylenically unsaturatedmono or polycarboxylic acids. Acrylic acid, methacrylic acid, crotonicacid, maleic acid and fumaric acid are examples of such acids. Thepreferred acid is methacrylic acid.

The elastomers useful in this invention have a second order glasstransition temperature (Tg) of less than -25° and are soluble in themonomers described hereinabove. Useful elastomers are synthetic highpolymers which exhibit plastic flow. The preferred elastomers are thosewhich are supplied commercially as adhesive or cement grades.

A preferred class of elastomers for use in this invention arepolychloroprene and copolymers of butadiene or isoprene with styrene,acrylonitrile, acrylate esters, methacrylate esters, and the like.Additional useful elastomers are copolymers of ethylene and acrylateesters, homopolymers of epichlorohydrin and copolymers ofepichlorohydrin and ethylene.

Specific examples of useful polymers using their letter designationaccording to ASTM D1418, their trade or common name and chemicaldescription are: CR-Neoprene-polychloroprene; NBR-Nitrilerubber-butadiene acrylonitrile copolymer containing about 25 to about 45weight percent acrylonitrile; COX--Hycar 1072-butadiene-acrylonitrilecopolymer modified with carboxylic groups; SBR-GR-S-styrene-butadienecopolymer containing about 10 to about 30 weight percent styrene;ABR--Acrylic rubber acrylate butadiene copolymer; and CO, ECO-Hydrin 100and 200-homopolymer or a copolymer of epichlorohydrin and ethyleneoxide. Additional useful elastomers are copolymers of ethylene andacrylate esters, such as methyl acrylate and ethyl acrylate, wherein thecopolymer contains at least 30 weight percent acrylate ester whichelastomers are sold commercially by duPont under the Vamac trademark.

Elastomers useful in this invention are described in detail in the"Handbook of Plastics and Elastomers" pages 1-106-119, (1975)McGraw-Hill, Inc., which is hereby incorporated by reference.

Particularly useful elastomers are polychloroprene and block copolymersof styrene and butadiene or isoprene, such block copolymers being soldunder the trademark Kraton by Shell Oil Company. Block copolymers ofstyrene and diene monomers are described in detail in U.S. Pat. Nos.4,041,103 and 4,242,470 which are hereby incorporated by reference.

Other elastomeric polymers having a Tg below -25° C. and solubility inthe methyl methacrylate monomer can be employed since, other than thelow Tg and solubility characteristics, there are no other limitations onthe identity of the elastomers except for the specific requirements ofthe particular adhesive being formulated, such as suitable molecularweight, viscosity characteristics and compatibility with the otheringredients of the adhesive.

Useful elastomers are those which are soluble in the monomers used inthe adhesives of this invention. These elastomers can form solutions offrom about 10 to about 35 weight percent elastomer in methylmethacrylate. As used herein the term "solution" is intended to covernot only true solutions but colloidal dispersion which exhibit normal orsubstantially newtonian rheology characteristics.

The core-shell graft copolymers useful in this invention have a"rubbery" core, a "hard" shell, and swell in the monomer compositionsbut do not dissolve therein. The "core" or backbone polymer of the graftcopolymers has a glass transition temperature substantially belowambient temperatures. The "shell" polymer which is grafted onto thebackbone polymer has a glass transition temperature substantially aboveambient temperatures. Ambient temperature is defined as the temperaturerange in which the adhesive is used.

Examples of useful core-shell graft copolymers are those where "hard"monomers, such as styrene, acrylonitrile or methyl methacrylate, aregrafted onto a rubbery core made from polymers of "soft" or"elastomeric" monomers, such as butadiene or ethyl acrylate.

U.S. Pat. No. 3,985,703, which is hereby incorporated by reference,describes useful core-shell polymers, the cores of which are madepreferably from butyl acrylate but can be based on ethyl, isobutyl,2-ethylhexyl, or other alkyl acrylates or mixtures thereof. The corepolymer, optionally, can contain up to 20 percent of othercopolymerizable monomers, such as styrene, vinyl acetate, methylmethacrylate, butadiene, isoprene and the like. The core polymeroptionally, can contain up to 5 percent of a crosslinking monomer havingtwo or more nonconjugated double bonds of approximately equalreactivity, such as ethylene glycol diacrylate, butylene glycoldimethacrylate and the like. It also optionally can contain up to 5percent of a graft-linking monomer having two or more nonconjugateddouble bonds of unequal reactivity, such as diallyl maleate and allylmethacrylate.

The shell stage is preferably polymerized from methyl methacrylate andoptionally other lower alkyl methacrylates, such as ethyl, butyl, ormixtures thereof. Up to about 40 percent by weight of the shell monomerscan be styrene, vinyl acetate, vinyl chloride, and the like.

Additionally useful core-shell graft copolymers are described in U.S.Pat. Nos. 3,984,497, 4,096,202, and 4,034,013, which are herebyincorporated by reference.

Still other useful core shell polymers are the "MBS" polymers such asthose described in U.S. Pat. No. 4,304,709 which is hereby incorporatedby reference. The MBS polymers are made by polymerizing methylmethacrylate in the presence of polybutadiene or a polybutadienecopolymer rubber.

Other patents which describe various useful core-shell graft copolymersare U.S. Pat. Nos. 3,944,631, 4,306,040 and 4,495,324, each of which ishereby incorporated by reference.

The core-shell graft polymers used in this invention swell in size inthe adhesive formulation but do not dissolve. The adhesives, soformulated, exhibit improved spreading and flow properties which arehighly desirable in many adhesive applications. For example, when anadhesive is applied to an article by means of a syringe-typeapplication, many adhesives "string-out" between the point where theapplicator was applied and the next position of the applicator. With thepresent invention, a small drop of adhesive can be applied to thearticle to be bonded with no adhesive string forming.

Additional components of the composition of this invention arepolymerization catalysts with or without other components which enhancethe reactivity of the catalysts. The catalysts are free radicalgenerators which trigger the polymerization of acrylate and methacrylatecompounds. Such catalysts are peroxides, hydroperoxides, peresters,peracids, radiant energy, e.g., ultraviolet light, and heat. Examples ofthese catalysts are benzoyl peroxide, cumene hydroperoxide, tertiarybutyl hydroperoxide, dicumyl peroxide, tertiary butyl peroxide acetate,tertiary butyl perbenzoate, ditertiary butyl azodiisobutyronitrile andthe like. These free radical producing catalysts are used in amounts ofabout 0.01 to about 10 weight percent based on the weight of theadhesive composition. Preferably, the catalysts will be used in theamount of about 0.05 to about 3 weight percent.

Other components which enhance the reactivity of the catalysts areinitiators or activators and promoters. Initiators and activators, whichterms are used interchangeably, include tertiary amines andaldehyde-amine reaction products. Useful tertiary amines includeN,N-dimethylaniline, N,N-dimethyltoluidine, N,N-diethylaniline,N,N-diethyltoluidine and the like. Aldehyde-amine reaction productsinclude such compositions as butyraldehyde-aniline andbutyraldehyde-butylamine compositions.

A promoter is an organic salt of a transition metal, such as cobalt,nickel, manganese or iron naphthenate, copper octoate, copperacetylacetonate, iron hexoate, or iron propionate.

The initiators or activators, if used, are added in the amount of up toabout 15 weight percent based on the weight of the adhesive. Preferredamounts are 0.01 to about 5 percent. Promoters are used in amounts up toabout 0.5 weight percent, preferably about 1 part per million to about0.5 weight percent.

The compositions of this invention are usually prepared in two partswherein 1 part contains the free radical catalysts and the other partcontains the initiator or activator and the promoter if it is used. Justprior to use, the two parts are mixed together and the mixture isapplied to at least one of the surfaces to be bonded. Alternatively, thepart containing the catalyst can be applied to one surface and the partcontaining the activator can be applied to the other surface. Whenpressed together, the two parts mix together and polymerization withresultant adhesive bonding takes place.

The adhesive compositions of this invention will contain about 55 toabout 75 weight percent methacrylate ester monomer, 0 to about 15 weightpercent acid monomer, about 5 to about 20 weight percent elastomer andabout 10 to about 30 weight percent core-shell graft copolymer, saidweight percents being based on the total weight of the components.Preferably, the compositions contains about 60 to about 70 weightpercent methacrylate ester monomer, about 2 to about 10 weight percentacid monomer, about 8 to about 15 weight percent elastomer and about 15to about 20 weight percent core-shell graft copolymer.

The adhesive compositions of this invention have high adhesive bondimpact strength (>15 ft-lb/sq.in) and high bulk tensile elongation (>10percent) when measured at -10° F. (-23° C.) or below. The bulk tensileelongation of these compositions is largely reversible even at low testtemperatures. This reversible high elongation contributes to thesuperior performance of these adhesives in structures which undergoimpacts at low temperatures.

The compositions of this invention are particularly useful for bondingthermoplastic automobile bumpers which must pass simulated crash impacttests at -10° to -20° F. (-23° to -29° C.) In these tests, which measureenergy management capability, bumpers are mounted horizontally and areimpacted at various positions and angles with a pendulum or hydraulicram at a rate that simulates a 2.5 or a 5 mile per hour crash. In thistest, the bumper and the adhesive bondline experience both high impactforces and a deflection of as much as 3 or 4 inches at the center. Afterthe test, the bumper springs back to its original shape. The high impactstrength and high elongation, especially reversible elongation at lowtemperatures, of the compositions of this invention are clearlyadvantageous in this bumper application.

The combination of relatively high modulus up to temperatures of 180° F.(82° C.) and high impact strength and elongation at temperatures of -10°F. (-23° C.) or below is very advantageous for bumpers and otherstructural applications which require high stiffness and structuralintegrity together with resistance to impact and other high stresses.

In the following examples, the elastomers were dissolved in the monomersby mixing until a uniform solution was obtained and no visible rubberparticles were present. The other components, e.g., the core-shellpolymers were then added to the elastomer solution and were stirreduntil a coarse paste was formed. Further mixing with a high sheardispersion apparatus was continued until a smooth paste was obtained.

Adhesive strength tests were performed by mixing the formulations with aperoxide catalyst paste, or by combining two adhesive polymer-in-monomersolutions, one of which contained a peroxide, the other a catalystactivator.

The adhesives were tested as follows:

LAP SHEAR STRENGTH (ASTM D-1002)

The adhesive shear strength of bonds formed between substrates, e.g., apolycarbonate/polyester thermoplastic resin (Xenoy, obtained fromGeneral Electric Company), was measured by applying sufficient adhesiveto one end of a 25 mm×76 mm×6.3 mm coupon of the substrate to completelyfill a 25 mm×12.5 mm×0.25 mm bond gap. A 0.25 mm wire shim or washer wasused to control bond thickness. A second coupon was placed over thecoupon coated with adhesive to provide the proper lap shearconfiguration in a mold designed to properly align the specimen.

After a cure time of 24 to 48 hours at room temperature, the bonds weretested at a separation rate of 1.27 mm per minute.

IMPACT STRENGTH (ASTM D-950)

The impact strength of the adhesives was tested using the procedure ofASTM D-950 except that steel bars or rods having diameters of 12.7 mmand lengths of 76.2 mm and 9.5 mm, respectively, were used instead ofthe test specimens having dimensions specified in the ASTM testingmethod. Surfaces to be bonded together were first solvent cleaned andthen grit blasted. After being bonded, the specimens were conditionedfor two days at room temperature prior to testing.

BULK ADHESIVE STRESS - STRAIN (ASTM B-638)

Sufficient adhesive components were mixed to form a sheet of curedadhesive approximately 2.5 mm in thickness from which tensile test"dumbbells" were cut using a metal die as specified in the ASTM testingmethod. Unless otherwise specified, the stress-strain tests wereperformed at the indicated temperatures using a separation rate of 5 mmper minute.

COLD IMPACT TEST ON PLASTIC SUBSTRATES

This test was devised to simulate the impact and deflection forces thatbonded structural assemblies, such as bumpers, experience under testconditions. This test was useful in evaluating the effect of"squeeze-out" at bond edges on the impact performance of the overallbonded assemblies. If the cured adhesive is not sufficiently elastic torelax under impact and elongation conditions, a crack can initiate inthe adhesive bead and propagate through the bonded assembly, leading tofailures.

In conducting the tests, a 15.2 cm long 5 gram bead of mixed adhesivewas applied lengthwise on the centerline of a 15.2 cm×2.5 cm plasticcoupon. A 2.5 cm length of 1.3 mm diameter stainless steel wire wasplaced approximately 6 mm from each end parallel to the plastic andperpendicular to the bead of adhesive. A 15.2 cm×1.3 cm plastic stripwas pressed down onto the adhesive until it made contact with the wire.The bonded assembly was allowed to cure at room temperature for at least24 hours.

Before testing, the assembly was placed in a -10° F. (-23° C.) freezerfor at least 15 hours. The cold sample was tested by placing it in amodified National Forge Model TM 52004 Izod-Charpy impact tester fittedwith a 10 ft/lb hammer. A fixture was used to hold the sample at eachend with the 2.5 cm plastic strip facing the impact hammer and thehammer was allowed to impact the plastic. The area of the hammer whichcontacts the plastic is approximately 1 cm². At the lowest point in theswing where the assembly is impacted, the hammer is travelling at 11feet per second. If, after the hammer impacts the cold plastic, thehammer rebounds and the test specimen remains intact, the result isrecorded as a pass. If the plastic breaks at the point of impact, theresult is recorded as a failure. Occasionally, the hammer impacts theplastic and rebounds, but the end of the plastic in the fixture cracks.This is recorded as an "end crack". It is considered a qualified pass,since the action of the fixturing assembly against the plastic imposesextraordinary stresses on the bonded assembly at these fulcrum points.

The components used in the examples are identified as follows:

    ______________________________________                                        MMA    Methyl methacrylate monomer containing 22-28 ppm of                           hydroquinone inhibitor                                                 MAA    Methacrylic acid containing 250 ppm of                                        hydroquinone inihibitor                                                BMA    Butyl methacrylate                                                     2-EHMA 2-Ethylhexyl methacrylate                                              Neo-   Polychloroprene homopolymer having a Brookfield                        prene  solution viscosity (5 weight percent in toluene)                              of about 20 to 35 mPa as measured on Model LVT                                visometer with UL adaptor                                              Nitrile                                                                              Carboxy modified butadiene-acrylonitrile elastomer                     Rubber with medium acrylonitrile content, specific                                   gravity of 0.98 and Mooney viscosity ML-4, 212° F.                     of 30-45                                                               Hypalon                                                                              Chlorosulfonated polyethylene containing 43                            30     percent chlorine and 1.1 percent sulfur - duPont                       Paraloid                                                                             Core-shell polymer of methacrylate-butadiene -                         KM 753 styrene with high butadiene content - Rohm & Haas                      Paraloid                                                                             All acrylic core-shell polymer - Rohm & Haas                           KM 330                                                                        Geloy  Core-shell polymer of acrylate rubber core and                         1020   styrene-acrylonitrile shell                                            Hydrin Liquid epichlorohydrin homopolymer with a                              10 × 1                                                                         Brookfield viscosity (27° C.) of 2.5 × 10.sup.5 cps,             a Tg                                                                          of -25° C. and a number average molecular weight of                    4,000.                                                                 DMT    N,N-dimethyl-p-tolidine                                                ZMTI   Zinc 2-mercaptotoluimidazole                                           VAMAC  ethylene-methyl acrylate copolymer gum-duPont                          KRA-   styrene-isoprene branched copolymer-                                   TON    Shell Oil Co.                                                          D 1320x                                                                              Oil Co.                                                                TYRIN  Chlorinated polyethylene containing 42% chlorine,                             Dow Chemical Co.                                                       DPESC  Diphenyl ether disulfonyl chloride                                     BHT    2,6-Di-tert butyl p-cresol                                             CHP    Cumene hydroperoxide, 80 weight percent in cumene                      BPO    A paste of 55 percent benzoyl peroxide in benzyl                       Paste  butyl phthalate plasticizer                                            VANAX  Butyraldehyde-aniline condensation product - R..                       808    Vanderbilt Co.                                                         ______________________________________                                        The Peroxide Paste used in the examples was prepared as follows: Hydrin       10×1, 25 parts by weight, and trioctyl trimellitate plasticizer, 25     arts by weight, were placed in a plastic container and were heated to         110° F. (43° C.). KM 753, 10 parts was gradually added as       the mixture was sheared with a laboratory Hochmeyer high shear mixture.       After all the KM 753 had been added, shearing was continued for 5             minutes. The mixture was then placed in a 110° F. (43° C.)      oven for one hour and was again sheared until a smooth paste was              obtained. After cooling, the BPO paste, 40 parts, was added and the       

The following tables list components used to formulate adhesivecompositions and show test results of cured adhesives. In preparing theadhesives, the Neoprene, nitrile rubber and Hypalon elastomer weredissolved in MMA to give solutions of 20, 25 and 40 weight percent,respectively. All other ingredients were combined by direct addition andwere mixed as described hereinbefore.

The examples which have A and B parts are two part adhesives which arecombined in a 1:1 weight ratio just prior to use. In the other examples(the 1 part adhesives), the Peroxide Paste was added prior to use, themix ratio being 1:10 paste to adhesive.

Table I illustrates greatly improved cold elongation of the compositionsof this invention, Ex 1 and 2, compared to a prior art example, Ex 3.

                  TABLE I                                                         ______________________________________                                                              3                                                       Example      1        2         A     B                                       ______________________________________                                        Composition                                                                   parts by wt                                                                   MMA          62.85    60.25     54.40 74.65                                   MAA          5.0      5.0       9.7                                           Neoprene     11.4                                                             Nitrile rubber        14.0                                                    Hypalon 30                      23.3                                          Paraloid KM 753                                                                            20.0     20.0      12.05                                         Paraloid KM 330                       8.2                                     Geloy 1020                            9.6                                     DMT          0.75     0.75                                                    CHP                             0.3                                           BHT                             0.25                                          Vanax 808                             7.55                                    Peroxide Paste                                                                             10       10                                                      Stress/Strain                                                                              5300     4800            6000                                    at -11 ± 1° F.                                                      (-24 ± .5° C.)                                                      Tensile strength                                                              at break, psi                                                                 Elongation at break                                                           % Average    23       30              9                                       % Maximum    26       44              12                                      Tg, °C. of elastomer                                                                -39      -20 & -30 10° C.                                 ______________________________________                                    

Table II illustrates the improvement in impact resistance at lowtemperatures of plastic assemblies bonded with the compositions of thisinvention, Ex 4 and 5, compared with a prior art composition, Ex 6. Thesteel impact test results show that Ex 4, 5 and 6 have similar impactstrengths when measured by conventional methods.

                  TABLE II                                                        ______________________________________                                                           5       6                                                  Example         4        A      B    A    B                                   ______________________________________                                        Composition                                                                   parts by wt                                                                   MMA             62.5     61.05  72.05                                                                              54.40                                                                              74.65                               MAA             5.0      9.6         9.7                                      Neoprene        11.35    11.05  11.25                                         Hypalon 30                           23.3                                     Paraloid KM 753 19.9     14.45  14.75                                                                              12.05                                    Paraloid KM 330                           8.2                                 Geloy 1020                                9.6                                 DMT             0.75            1.95                                          CHP                                  .3                                       BHT                                  .25                                      ZMTI            0.5                                                           Vanax 808                                 7.55                                Peroxide Paste  10                                                            BPO Paste                3.85                                                 Lap Shear Stgth, psi                                                                              1555     1595    1460                                     on Xenoy 1102                                                                 Cold Impact Test                                                                          Pass    6        4       1                                        on Xenoy 1102                                                                             Fail    0        1       5                                        -12 ± 2° F.                                                                     Crack   0        1       0                                        (-24.5 ± 1° C.)                                                     Steel Impact Stgth. 19.5     23.1    22.0                                     ______________________________________                                    

Table III lists additional examples of adhesive compositions whichprovide adhesives with high elongation and resistance to low temperatureimpact failures when used to bond plastic. Examples 7 and 8 are madeusing elastomers having Tg's of less than -25° C., Example 9 uses anelastomer having a Tg higher than -25° C.

                  TABLE III                                                       ______________________________________                                                    7       8         9                                               Example       A      B      A    B    A    B                                  ______________________________________                                        Composition                                                                   parts by weight                                                               MMA           35.5   73.5   35.5 73.5 35.5 73.5                               BMA           14            14        14                                      2-EHMA        14            14        14                                      MAA           10            10        10                                      VAMAC G       11.5   11.5                                                     KRATON                      11.5 11.5                                         TYRIN                                 11.5 11.5                               Paraloid KM 753                                                                             15     15     15   15   15   15                                 DMT                  2           2         2                                  BPO PASTE     4             4         4                                       Elongation    17        20        5                                           % at -11 ± 1° F.                                                    (-24 ± .5° C.)                                                      Steel impact Test                                                                           24.4      21.0      8.9                                         ft-lb/in.sup.2 at -20° F.                                              (-29° C.)                                                              Cold impact test                                                                            83        100       17                                          on Xenoy 1102,                                                                -12 ± 2° F.                                                         (-24 ± .5° C.)                                                      % passed                                                                      Tg, °C. of Elastomer                                                                 -27.8     -56       +10                                         ______________________________________                                    

The examples listed in Table IV show additional adhesive tested at lowtemperatures. The Example 10 adhesive contains a core-shell polymer butno low Tg elastomer. Example 11 has a core-shell polymer and anelastomer having a Tg above -25° C. Example 12 has a low Tg elastomerbut no core-shell polymer. Example 13 contains a low Tg elastomer and nocore-shell polymer. This adhesive exhibits decreased bonding strength onXenoy plastic as shown in Table V. Example 14 contains both a low Tgelastomer and a core-shell polymer.

                  TABLE IV                                                        ______________________________________                                                                 14                                                   Example    10      11      12    13    A    B                                 ______________________________________                                        Composition                                                                   part by weight                                                                MMA        62.85   62.85   69.27 62.85 62.60                                                                              66.74                             MAA        5.0     5.0     5.0   5.0   9.68                                   Neoprene                   24.98       11.15                                                                              11.15                             Nitrile rubber                   31.4                                         Hypalon 30         11.4                                                       Paraloid KM 753                                                                          31.4    20.0                14.56                                                                              14.56                             DMT        0.75    0.75    0.75  0.75                                         CHP                                    0.3                                    BHT                                    0.25                                   Vanax 808                                    7.55                             DPESC                                  1.46                                   Peroxide Paste                                                                           10      10      10    10                                           Stress/Strain                                                                            6031    6980    3029  5025  4975                                   at -11 ± 1° F.                                                      (-24 ± .5° C.                                                       Tensile Stgth                                                                 at break, psi                                                                 Elongation at                                                                 break                                                                         % AVG      <5%     <5%     6%    52%    11                                    MAX        <5%     <8%     6%    70%   16%                                    Tg °C. of   +10     -34.3 -20 & -34.3                                  elastomer                        -30                                          ______________________________________                                    

The examples listed in Table V illustrate the decrease in adhesion toXenoy plastic with increasing levels of nitrile rubber. Example 15 whichcontains the highest amount of nitrile rubber and no core shell polymerhas the lowest Lap Shear Strength on Xenoy plastic. Examples 16 and 17,which contain elastomer and core-shell polymer within the limits of theinvention, have good tensile strength elongation at break and adhesionto Xenoy plastic. Example 18 which contains less elastomer than claimedin the invention has good tensile strength and adhesion but poorelongation at break.

                  TABLE V                                                         ______________________________________                                        Example       15      16       17     18                                      ______________________________________                                        Composition                                                                   parts by weight                                                               MMA           70.9    60.3     58     63.4                                    MAA           5       5        5      5                                       Nitrile rubber                                                                              23.6    14.1     6.5    1.3                                     Paraloid KM 753       20.1     30     29.8                                    DMT           .5      .5       .5     .5                                      Stress/Strain                                                                 at -11 ± 1° F.                                                      (-23 ± .5° C.)                                                      Tensile Strength      4590     5040   6400                                    at break, psi                                                                 Elongation at                                                                 break                                                                         % AVG                 18       15     4                                       % MAX                 25       15     5                                       Lap Shear Strength, psi                                                                             1480     1615   1663                                    965                                                                           ______________________________________                                    

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed, sincethese are to be regarded as illustrative rather than restrictive.Variations and changes may be made by those skilled in the art withoutdeparting from the spirit of the invention.

What is claimed is:
 1. An adhesive composition comprising:(a) about 55to about 75 weight percent methyl methacrylate; (b) 0 to about 15 weightpercent methacrylic acid; (c) about 5 to about 20 weight percentpolychloroprene which is soluble in methyl methacrylate and which has aTg below about -25° C.; and (d) about 10 to about 30 weight percent of acore-shell graft copolymer which has a butadiene-styrene core and amethyl methacrylate shell and which swells in the monomer but does notdissolve therein, wherein said weight percents are based on the totalweight of (a), (b), (c) and (d).
 2. The adhesive composition of claim 1wherein the methyl methacrylate is present in the amount of about 60 toabout 70 weight percent, the methacrylic acid is present in the amountof about 2 to about 10 weight percent, the polychloroprene is present inthe amount of about 8 to about 15 weight percent, and the core-shellgraft copolymer is present in the amount of about 15 to about 20 weightpercent.
 3. An adhesive composition comprising:(a) about 55 to about 75weight percent methyl methacrylate; (b) 0 to about 15 weight percentmethacrylic acid; (c) about 5 to about 20 weight percent nitrile rubberwhich is soluble in methyl methacrylate and which has a Tg below about-25° C.; and (d) about 10 to about 30 weight percent of a core-shellgraft copolymer which has a butadiene-styrene core and a methylmethacrylate shell and which swells in the monomer but does not dissolvetherein, wherein said weight percents are based on the total weight of(a), (b), (c) and (d).
 4. The adhesive composition of claim 3 whereinthe methyl methacrylate is present in the amount of about 60 to about 70weight percent, the methacrylic acid is present in the amount of about 2to about 10 weight percent, the nitrile rubber is present in the amountof about 8 to about 15 weight percent and the core shell graft copolymeris present in the amount of about 15 to about 20 weight percent.
 5. Anadhesive composition comprising:(a) about 55 to about 75 weight percentmethyl methacrylate; (b) 0 to about 15 weight percent methacrylic acid;(c) about 5 to about 20 weight percent of a block copolymer of butadieneor isoprene and styrene which is soluble in methyl methacrylate andwhich has a Tg below about -25° C.; and (d) about 10 to about 30 weightpercent of a core-shell graft copolymer which has a butadiene-styrenecore and a methyl methacrylate shell and which swells in the monomer butdoes not dissolve therein, wherein said weight percents are based on thetotal weight of (a), (b), (c) an (d).
 6. The adhesive composition ofclaim 5 wherein the methyl methacrylate is present in the amount ofabout 60 to about 70 weight percent, the methacrylic acid is present inthe amount of about 2 to about 10 weight percent, the block copolymer ispresent in the amount of about 8 to about 15 weight percent, and thecore-shell graft copolymer is present in the amount of about 15 to about20 weight percent.